# CP Symmetry

## Concrete

Kaon Flavor Eigenstates:

\begin{equation*} |K^0\rangle = |\bar{s}d \rangle \qquad |\overline{K}^0\rangle = |s \bar{d} \rangle \end{equation*} $$CP\!: \; |K^0\rangle \longleftrightarrow |\overline{K}^0 \rangle$$

Kaon CP Eigenstates:

\begin{equation*} |K_{CP \pm}\rangle = \frac{1}{\sqrt{2}} \left( |K^0\rangle \pm |\overline{K}^0 \rangle \right) \end{equation*}

Kaon Propagating Mass Eigenstates:

$$|K_L \rangle \sim |K_{CP-}\rangle + \epsilon_K |K_{CP+}\rangle$$

Observables:

CP Violation in the Neutrino Sector

## Why is it interesting?

A CP transformation transforms a particle into the corresponding antiparticle. A intact CP symmetry therefore means that particles and antiparticles are indistinguishable. However, we know from experiments that CP is a broken symmetry since, for example, there are more particles than antiparticles in the visible universe.